WO2018190311A1 - Mechanical pencil - Google Patents

Abstract

[Problem] To provide a mechanical pencil comprising a cushion spring by which a plurality of cushion action regions that exhibit cushion action with different spring constants are connected without jumping. [Solution] A mechanical pencil according to one embodiment comprises: a shaft; a clutching mechanism that is housed within the shaft and is capable of holding and propelling a lead; and first and second cushion springs that elastically support the clutching mechanism in the axial direction with respect to the shaft. The first and second cushion springs are combined to form a first cushion action region that has a first spring constant and a second cushion action region that has a second spring constant. The first and second cushion action regions are connected without jumping.

Description

mechanical pencil

The present invention relates to a mechanical pencil provided with a chuck for gripping a writing core and capable of feeding out the writing core by a knocking operation.

Conventionally, a lead tank slidably provided in the shaft cylinder, a chuck fixed to the tip of the lead tank, a chuck ring loosely fitted to the chuck, and a space between the shaft cylinder and the chuck A sleeve provided on the sleeve, an elastic body that comes into contact with the sleeve and a part of which is crimped to the core tank, and an operation for compressing the elastic body to move the core tank in the axial direction. A mechanical pencil composed of means is known (for example, see Patent Document 1).

JP-A-7-290880 (see, for example, paragraphs 0006 and 0017)

According to the mechanical pencil disclosed in Patent Document 1, a stroke for pushing out the slider can be sufficiently obtained with a simple structure in which the chuck tightening spring and the cushion spring are integrated. However, conventionally, for example, one region that cushions with a single spring constant to absorb excessive writing pressure and write, and another one that is different from the one spring constant to prevent breakage of the writing core. There has been a need to provide a mechanical pencil having a cushion spring in which a plurality of cushion operating areas that are cushioned with different spring constants, such as other areas that are cushioned with a spring constant, are connected without jumping.

An object of the present invention is to provide a mechanical pencil including a cushion spring in which a plurality of cushion operation areas that perform cushion operation with different spring constants are connected without jumping.

In one aspect of the mechanical pencil according to the present invention, the mechanical pencil includes a shaft cylinder, a chuck mechanism housed in the shaft cylinder, a chuck mechanism capable of gripping and feeding the writing core, and the chuck mechanism. A first cushion operation having a first spring constant by combining the first and second cushion springs, the first and second cushion springs being elastically supported in the axial direction with respect to the shaft cylinder. A region and a second cushion actuation region having a second spring constant are formed, and the first and second cushion actuation regions are connected without jumping.

In a plurality of aspects according to the present invention, it is possible to provide a mechanical pencil including a cushion spring in which a plurality of cushion operation regions that perform a cushion operation with different spring constants are connected without jumping.

It is a fragmentary sectional view which abbreviate | omits the intermediate part of the mechanical pencil which concerns on one Embodiment of this invention, and shows a front side part and a back side part. It is a diagram which shows the output load with respect to the displacement in the synthetic | combination cushion spring of the mechanical pencil which concerns on one Embodiment of this invention. It is a fragmentary sectional view which abbreviate | omits the intermediate part of the mechanical pencil which concerns on other embodiment of this invention, and shows a front side part and a back side part.

Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings. The mechanical pencil 1 of the present embodiment shown in FIG. 1 is a rear-end knock-type mechanical pencil in which a writing core T is sent out from the tip of the front end 3 by a knocking operation to the knock button 5 and protrudes. In the following description, the side on which the tip 3 of the mechanical pencil 1 is disposed is the front in the central axis direction (axial direction) extending in the longitudinal direction of the mechanical pencil 1, and the side on which the knock button 5 is disposed. This will be described as the rear.

The mechanical pencil 1 includes a shaft body 2 having a substantially cylindrical shape and a tip 3 having a generally tapered cylindrical shape. A shaft tube is formed including the shaft tube main body 2 and the tip 3. The tip 3 is disposed in front of the shaft body 2. The rear portion of the tip 3 is formed in a double cylinder shape having an outer cylinder 3a and an inner cylinder 3b. The front end 3 is formed on the outer peripheral surface of the front end portion of the shaft main body 2 with respect to the main shaft body 2 and on the inner peripheral surface of the outer tube 3 a behind the front end 3. The female screw portion 3a1 is fixed by screwing.

A knock button 5 formed in the shape of a bottomed cylinder is detachably assembled to the rear end of the core pipe 11 which will be described later in detail, which is arranged inside the shaft cylinder body 2. The inner peripheral surface of the front end opening of the knock button 5 is detachably fitted to the outer peripheral surface of the rear end of the core pipe 11. The outer peripheral surface of the front portion of the eraser holder 4 formed in a substantially cylindrical shape is removably fitted and assembled to the inner peripheral surface of the rear end of the core pipe 11. The eraser holder 4 has a small diameter part 4a on the front side and a large diameter part 4b on the rear side. The outer peripheral surface of the eraser 6 is detachably fitted to the inner peripheral surface of the large-diameter portion 4b of the eraser holder 4 and assembled.

The core pipe 11 that accommodates the writing core T therein is formed in a substantially cylindrical shape, and is arranged in the shaft body 2. A chuck 12 is assembled to the front portion of the core pipe 11. The chuck 12 is formed so that it can be gripped by pinching the writing core T in the radial direction when each of the chuck pieces formed by dividing the tip thereof into three in the circumferential direction is elastically deformed toward the central axis. Is done. The chuck 12 includes a base 12a at the rear end that is inserted into and fixed to the core pipe 11, a beam 12b that extends forward from the base 12a, and a bulge 12c that is formed at the front end of the beam 12b. And having. A chuck ring 13 is detachably attached to the outer periphery of the bulging portion 12c. A sleeve 7 is disposed on the outer periphery of the front portion of the core pipe 11 and the outer periphery of the base portion 12a and the beam-shaped portion 12b of the chuck 12 as shown in the figure.

The sleeve 7 is formed in a substantially cylindrical shape. An annular wall 7 a is formed on the inner peripheral surface of the front end portion of the sleeve 7 so as to protrude radially inward. On the other hand, on the outer peripheral surface of the front portion of the sleeve 7, an annular protrusion 7 b is formed to protrude radially outward. On the inner peripheral surface of the shaft tube main body 2, an annular projecting portion 2 b is formed to project radially inward so as to face the projecting portion 7 b of the sleeve 7 in the axial direction. A synthetic cushion spring 18, which is a compression coil spring that is compressed in the axial direction, is disposed between the protruding portion 7 b of the sleeve 7 and the protruding portion 2 b of the shaft cylinder body 2. The synthetic cushion spring 18 is supported with its front end in the axial direction in contact with the protruding portion 7b of the sleeve 7 and supported with its rear end in contact with the protruding portion 2b of the shaft cylinder body 2. In this way, the synthetic cushion spring 18 is disposed so as to extend in the axial direction between the sleeve 7 and the shaft body 2. The synthetic cushion spring 18 urges the sleeve 7 forward relative to the shaft body 2.

The synthetic cushion spring 18 is formed such that the number of coil turns per unit length is different between the area S1 on the front side and the area S2 on the rear side. In the present embodiment, a first winding portion 18-1 that functions as a first cushion spring is formed in the region S1, and a second winding portion 18- that functions as a second cushion spring is formed in the region S2. 2 is formed. The synthetic cushion spring 18 is formed by combining a first cushion spring and a second cushion spring, and is integrally formed as a coil spring having a first winding portion 18-1 and a second winding portion 18-2. . The spring constant of the first winding portion 18-1 in the region S1 in which the number of coil turns per unit length is larger than that in the region S2 is that in the region S2 in which the number of coil turns per unit length is smaller than that in the region S1. This is smaller than the spring constant of the second winding 18-2. This is because the number of turns per unit length of the first winding part 18-1 is larger than that of the second winding part 18-2, so that the extension direction of the coil spring wire (coil winding direction) is increased. This is because when the inclination angle with respect to the axial direction is increased, the first winding portion 18-1 is more easily bent with respect to the axial direction. In the present embodiment, the first winding portion 18-1 is wound at a winding pitch of about 0.1 mm.

A chuck spring 15 that is a coil spring is assembled between the outer peripheral surface of the beam-like portion 12 b of the chuck 12 and the inner peripheral surface of the sleeve 7. The front end of the chuck spring 15 abuts on the rear surface of the annular wall 7 a of the sleeve 7, and the rear end abuts on the front end surface of the core pipe 11. The chuck spring 15 is assembled while being compressed in the axial direction between the sleeve 7 and the core pipe 11. Since the core pipe 11 and the chuck 12 are urged rearward with respect to the sleeve 7 by the urging force of the chuck spring 15, the chuck ring 13 fitted to the chuck 12 is also urged with respect to the sleeve 7. As described above, the rear end surface of the chuck ring 13 and the front surface of the annular wall 7a of the sleeve 7 abut.

A plurality of ribs 3b1 extending in the axial direction are formed on the inner peripheral surface of the inner cylinder 3b of the tip 3 in the circumferential direction. The front end surface of the sleeve 7 abuts against the rear end surface of the rib 3b1 in a state of being biased forward by the synthetic cushion spring 18.

A step portion 3b2 that can abut when the front end surface of the chuck ring 13 advances is formed at a substantially central position in the axial direction of the rib 3b1. When the front end surface of the chuck ring 13 comes into contact with the step portion 3b2 of the rib 3b1 formed in the inner cylinder of the tip 3, the chuck ring 13 is detached rearward from the chuck 12 and the writing core T is released from gripping by the chuck 12. Is done. A series of feeding operations of the mechanical pencil 1 will be described in detail later.

A guide pipe 31 is disposed at a position in front of the front end face of the chuck 12 so as to be movable in the axial direction. The guide pipe 31 includes a disc-shaped base end portion 31b, a center hole through which the writing core T is inserted in the axial direction, and a plurality of insertion legs formed to protrude forward from the base end portion 31b around the center hole. 31a. The distal end of the insertion leg 31a is formed in a bowl shape as shown in the figure, and is engaged with a slit 32a formed in the core holder 32, which will be described in detail later. It is movably locked.

A step portion is formed on the outer peripheral edge of the base end portion 31 b of the guide pipe 31. Further, a step portion of the inner periphery of the tip 3 is formed on the inner peripheral surface of the tip 3 that faces the step of the base end portion 31 b of the guide pipe 31 in the axial direction. A return spring that is a compression coil spring that biases the guide pipe 31 toward the rear in the axial direction with respect to the front end 3 between the base end portion 31b of the guide pipe 31 and the stepped portion on the inner periphery of the front end 3. 36 is arranged. In a state where the guide pipe 31 is urged rearward by the return spring 36, the rear end surface of the base end portion 31b of the guide pipe 31 approaches the front end surface of the chuck 12 from the front. Further, when the chuck 12 moves forward, the rear end surface of the guide pipe 31 comes into contact with the front end surface of the chuck 12 from the front. The rear end surface of the guide pipe 31 supports the writing core T protruding from the front end surface of the chuck 12 in a direction orthogonal to the axial direction in a state in which the rear end surface of the guide pipe 31 is close to or in contact with the front end surface of the chuck 12. Therefore, the bending moment acting on the position on the front end surface of the chuck 12 in the axial direction of the writing core T gripped by the chuck 12 is reduced, and the writing core T breaks at the position of the front end surface of the chuck 12. Can be prevented.

A core holder 32 is disposed at a position in front of the guide pipe 31 so as to be movable in the axial direction. The lead holder 32 is formed with a plurality of slits 32a extending in the front-rear direction. The tip of the insertion leg 31a of the guide pipe 31 described above is slidably engaged with the slit 32a. As a result, the guide pipe 31 is locked to the lead holder 32 so as to be relatively movable in the front-rear direction. The core holder 32 is formed with a central hole through which the writing core T is inserted in the axial direction. A holding portion that holds the writing core T sandwiched radially inward is formed at the tip of the center hole of the core holder 32. In front of the core holder 32, there is an outer peripheral surface that slides with the inner peripheral surface of the opening 3c of the tip 3 that will be described in detail later, and a substantially tapered cylindrical tip pipe configured to be movable in the axial direction. 30 is arranged. The lead holder 32 is inserted into the tip pipe 30 from behind and assembled to the tip pipe 30.

鍔 A flange is formed at the rear end of the tip pipe 30. An O-ring 38 that elastically supports the tip pipe 30 and the core holder 32 in a direction orthogonal to the direction of the axis L is assembled to the outer periphery of the collar portion. The O-ring 38 is configured to provide appropriate sliding resistance against the movement of the tip pipe 30 and the core holder 32 in the front-rear direction. Here, the appropriate sliding resistance refers to sliding resistance that can hold the tip pipe 30 and the core holder 32 so that the drawn writing core T can be held in the axial direction. Further, when a larger axial pressing force is applied to the tip pipe 30 and the core holder 32, the tip pipe 30 protrudes from the tip 3 or the tip pipe 30 is stored in the tip 3. The sliding resistance that allows the movement of the tip pipe 30 and the core holder 32 is said. The forward movement of the tip pipe 30 and the core holder 32 is restricted by the flange portion of the tip pipe 30 coming into contact with the step formed on the inner peripheral surface of the opening 3c of the tip.

A chuck mechanism capable of gripping and feeding out the writing core T includes a chuck 12, a chuck ring 13, a sleeve 7, and a chuck spring 15, and is accommodated in the shaft cylinder. In this embodiment, the synthetic cushion spring 18 which is a coil spring that elastically supports the chuck mechanism in the axial direction is attached with a free length. With this configuration, it is possible to perform writing while absorbing excessive writing pressure according to the spring constant of the first cushion spring (first winding portion 18-1) of the synthetic cushion spring 18. It is possible to perform high-quality writing that reflects the spring constant of the first winding portion 18-1 that functions as the first cushion spring of the spring 18. On the other hand, when an excessive writing pressure is applied to the writing core T held by the chuck mechanism, the second winding portion 18-functioning as the second cushion spring of the synthetic cushion spring 18 having a relatively large spring constant. It can be prevented that 2 is bent and the writing core T is broken.

The feeding of the writing core T by the mechanical pencil 1 will be described. By the knocking operation of pressing the knock button 5, the core pipe 11, the chuck 12 fitted with the chuck ring 13 and the writing core T held by the chuck 12 are moved forward against the biasing force of the chuck spring 15. The guide pipe 31 that is in contact with the advanced chuck 12 is also pressed forward, and moves forward against the urging force of the return spring 36. When the guide pipe 31 moves forward, the lead holder 32 and the tip pipe 30 pressed by the guide pipe 31 move forward and protrude from the tip 3. When the chuck 12 and the chuck ring 13 are moved by a predetermined distance, the front end surface of the chuck ring 13 is engaged with the contact surface of the step portion 3b2 formed on the inner peripheral surface of the tip 3, and the bulging portion of the chuck 12 is engaged. The chuck ring 13 is detached from 12c toward the rear. When the chuck ring 13 is detached, each of the chuck pieces of the chuck 12 is elastically opened outward in the radial direction, and the writing core T is released. The writing core T is sent out by a predetermined feed amount per knock operation in the mechanical pencil 1 and released. When the pushing of the knock button 5 is released and the chuck mechanism is released from the knocking operation, the chuck 12 and the chuck ring 13 are moved backward while leaving the writing core T held by the lead holder 32 in the position where it is fed out and released. The position behind the writing core T before the knocking operation is again gripped. When the chuck mechanism is released from the knocking operation and the chuck 12 and the chuck ring 13 are retracted, the guide pipe 31 is urged by the return spring 36 and retracts.

The mechanical pencil 1 can be written with a predetermined amount of the writing core T protruding from the tip pipe 30. A load (so-called writing pressure) generated in the axial direction by writing is applied to the writing core T, the chuck 12 that holds the writing core T, the chuck ring 13, and the sleeve 7. In response to this writing pressure, the synthetic cushion spring 18 is elastically deformed, and a cushioning operation occurs in which the writing core T, the chuck 12, the chuck ring 13, and the sleeve 7 are moved backward with respect to the shaft body 2.

The cushion operation of this embodiment will be described with reference to FIG. FIG. 2 shows a specific example of the relationship between the writing pressure (load) in the cushion operation of the mechanical pencil 1 and the displacement amount (the compression amount or the operation amount of the synthetic cushion spring 18) by which the chuck 12 elastically supported by the synthetic cushion spring 18 moves backward. Indicates. When writing pressure is applied to the writing core T, the first winding portion 18-1 that is the first cushion spring of the synthetic cushion spring 18 is compressed to a greater extent in the initial stage, and the second cushion spring is obtained. The second winding 18-2 is also slightly compressed. At this time, the synthetic cushion spring 18 operates in a first cushion operation region CR1 shown by a diagram from point O to point P in FIG. When the writing pressure is applied by about 150 g, the synthetic cushion spring 18 contracts by about 0.45 mm. When the writing pressure exceeds about 150 g, the first winding portion 18-1 that is the first spring is brought into close contact, and only the second winding portion 18-2 that is the second spring is operated. It operates in the second cushion operation region CR2 shown in the following diagram. When the writing pressure is applied by about 350 g, the synthetic cushion spring 18 contracts by about 0.8 mm.

The synthetic cushion spring 18 has a first spring constant in the first cushion operation region CR1, and has a second spring constant different from the first cushion operation region CR1 in the second cushion operation region CR2. By combining the first and second cushion springs of the synthetic cushion spring 18, a first cushion operation region CR1 having a first spring constant, and a second cushion operation region CR2 having a second spring constant, Is configured. The first cushion operation region CR1 and the second cushion operation region CR2 are continuously connected as illustrated without further jumping. In other words, the compression amount and output at the end point of the first cushion operation region CR1 of the synthetic cushion spring 18 coincide with the compression amount and output at the start point of the second cushion operation region CR2. If comprised in this way, the user can use the mechanical pencil 1 without being conscious of the transition between several cushion action | operation area | regions which have a different spring constant.

The writing core T is usually used by protruding from the tip pipe 30 within a range of 0.45 ± 0.15 mm. As shown in this embodiment, when the synthetic cushion spring 18 is contracted in the range of 0.45 ± 0.15 mm when the writing pressure is applied in the range of 150 ± 50 g, the writing core T is made to be the tip pipe 30. It is preferable because the normal writing state of projecting from the first cushion operating region CR1 of the synthetic cushion spring 18 can be made substantially coincident. In this case, the first cushion operation region CR1 and the second cushion operation region CR2 are configured such that the first and second cushion springs combined when the writing pressure is applied in the range of 150 ± 50 g. It is connected without jumping at one operating point that shrinks in the range of 0.45 ± 0.15 mm. Further, for example, it is more preferable that the composite cushion spring 18 is contracted in the range of 0.45 ± 0.09 mm when the writing pressure is applied in the range of 150 ± 30 g, and the load is applied in the range of 150 ± 10 g. Most preferably, the composite cushion spring 18 is configured to contract within a range of 0.45 ± 0.03 mm when it is applied. When the operation amount (compression amount) of the synthetic cushion spring 18 is larger than the protruding amount of the writing core T from the tip pipe 30, the tip pipe 30 and the core holder 32 whose tips contact the writing surface are retracted. As far as possible, the distal end pipe 30 and the core holder 32 are retracted to secure the operation amount (compression amount) of the synthetic cushion spring 18. The tip pipe 30 and the lead holder 32 are retracted while protecting the writing lead T, and when the writing pressure is removed and the synthetic cushion spring 18 is restored to its free length, the writing lead T protrudes from the tip pipe 30 again. .

Further, as shown in the present embodiment, the synthetic cushion spring 18 may be configured to contract in the range of 0.8 ± 0.11 mm when the writing pressure is applied in the range of 350 ± 50 g. In this case, the end point assumed for normal writing in the second cushion operation region CR2 of the composite cushion spring 18 may be a displacement amount that allows the user to easily recognize an increase in the cushion stroke. This is preferable because the writing pressure can be reduced and the writing core T can be prevented from being broken. In this case, the second cushion operation region CR2 has a range in which the combined first and second cushion springs are in the range of 0.8 ± 0.11 mm when the writing pressure is applied in the range of 350 ± 50 g. Includes one operating point that shrinks at Further, for example, it is more preferable that the composite cushion spring 18 is contracted in the range of 0.8 ± 0.07 mm when the writing pressure is applied in the range of 350 ± 30 g, and the load is applied in the range of 350 ± 10 g. It is most preferable that the synthetic cushion spring 18 is configured to contract within a range of 0.8 ± 0.02 mm.

In another embodiment, the second cushion operating region CR2 is configured to have a spring constant smaller than that of the present embodiment, and the second cushion operating region is compressed when the synthetic cushion spring 18 is compressed by about 1.5 mm. It is good also as what is comprised so that the end point assumed for normal writing in CR2 may be located. In this case, the user not only prevents the writing core T from being broken in the second cushion operation region CR2 having a longer cushion stroke, but also the second cushion spring (second winding portion 18-) of the synthetic cushion spring 18. High-quality writing that reflects the spring constant of 2) can be performed.

In this way, it is possible to provide a mechanical pencil including a cushion spring in which a plurality of cushion operation regions that operate with different spring constants are connected without jumping. Since the synthetic cushion spring 18 is integrally formed as a coil spring having the first winding portion 18-1 and the second winding portion 18-2 having different winding numbers, it can be suitably formed with a reduced number of parts. it can. Further, since the synthetic cushion spring 18 is attached with a free length, as shown in FIG. 2, the cushion operation can be performed in the entire operation region of the synthetic cushion spring 18 including the point O.

A mechanical pencil 1A according to another embodiment of the present invention will be described with reference to FIG. The mechanical pencil 1A is the same as the mechanical pencil 1 described above except for the configuration of the synthetic cushion spring 18A. For this reason, regarding the mechanical pencil 1A, only the synthetic cushion spring 18A will be described, and redundant description will be omitted. The synthetic cushion spring 18A of the mechanical pencil 1A includes a first cushion spring 18A-1 having a relatively small diameter, which is formed separately from each other, and a relatively large diameter disposed on the outer periphery of the first cushion spring 18A-1. And a large second cushion spring 18A-2. As described above, the first cushion spring 18A-1 and the second cushion spring 18A-2, which are formed separately from each other, may be arranged in parallel to constitute the composite cushion spring 18A. On the other hand, in the synthetic cushion spring 18 of the mechanical pencil 1 of the above-described embodiment, the first cushion spring (first winding portion 18-1) and the second cushion spring (second winding portion 18-2). Are arranged in series.

The first cushion spring 18A-1 and the second cushion spring 18A-2 of the synthetic cushion spring 18A of the present embodiment have different spring constants. The first cushion spring 18A-1 wound at one predetermined equal interval pitch is supported in a state where its front end in the axial direction is in contact with the protruding portion 7b of the sleeve 7, and its rear end is the shaft cylinder body 2. It is supported in a state of being in contact with the protruding portion 2b. The second cushion spring 18A-2 wound at another predetermined equal pitch is supported in a state where the rear end in the axial direction is adhered to the front surface of the protruding portion 2b of the shaft cylinder body 2. The front end is arranged so as not to contact the protruding portion 7 b of the sleeve 7. With this configuration, only the first cushion spring 18A-1 operates at the initial stage of the operation of the synthetic cushion spring 18A. When further writing pressure is applied, after the first cushion spring 18A-1 is elastically deformed by a predetermined amount and operated, the tip of the second cushion spring 18A-2 comes into contact with the rear surface of the protruding portion 7b of the sleeve 7. . Thereafter, when further writing pressure is applied, both the first cushion spring 18A-1 and the second cushion spring 18A-2 are elastically deformed to operate. For this reason, it is possible to provide a mechanical pencil including a cushion spring that is connected without jumping a plurality of cushion operation regions that perform cushion operation with different spring constants.

The relationship between the writing pressure (load) in the cushion operation of the synthetic cushion spring 18A of this embodiment and the displacement amount (the compression amount or the operation amount of the synthetic cushion spring 18A) of the chuck 12 elastically supported by the synthetic cushion spring 18A is as follows. This is the same as the case of the mechanical pencil 1 shown in FIG. When writing pressure is applied to the writing core T, only the first cushion spring 18A-1 is initially compressed in the synthetic cushion spring 18A, and the second cushion spring 18A-2 does not operate. At this time, the synthetic cushion spring 18A operates in a first cushion operation region CR1 shown by a diagram from point O to point P in FIG. When the writing pressure is applied to about 150 g, the synthetic cushion spring 18A contracts by about 0.45 mm. When the writing pressure exceeds about 150 g, the second cushion spring (second winding portion 18-2) operates together with the first cushion spring (first winding portion 18-1). 2 operates in the second cushion operation region CR2 shown by the diagram after the point P in FIG. The spring constant in the second cushion operation region CR2 of the synthetic cushion spring 18A is configured to be larger than the spring constant in the first cushion operation region CR1. For this reason, the user can easily grasp the operation of the synthetic cushion spring 18A in the second cushion operation region CR2 by the rate of increase of the writing pressure (spring constant) at the time of writing. When the writing pressure is applied by about 350 g, the synthetic cushion spring 18A contracts by about 0.8 mm.

Although a plurality of embodiments of the present invention have been described above, the present invention is not limited to these embodiments and can be implemented with various modifications. For example, in the above-described embodiment, the synthetic cushion spring 18 has been described as including one coil spring having the first winding portion 18-1 and the second winding portion 18-2. However, the present invention is not limited to this, and the first cushion spring and the second cushion spring formed separately may be arranged in series to constitute a synthetic cushion spring. For example, the spring constant of the first winding portion 18-1 may be configured to be larger than the spring constant of the second winding portion 18-2. As described above, the first and second cushion springs arranged in series can be arbitrarily arranged by being exchanged. Furthermore, the synthetic cushion spring is not limited to the first and second cushion springs described above, and may have a plurality of arbitrary two or more cushion springs, and may be configured to operate in combination. The synthetic cushion spring has been described as being formed as a coil spring. However, the present invention is not limited thereto, and an elastic resin, rubber, or the like may be molded into an arbitrary shape and used.

DESCRIPTION OF SYMBOLS 1,1A Mechanical pencil 2 Shaft cylinder main body 2a Male thread part 2b Projection part 3 Front port 3a Outer cylinder 3a1 Female thread part 3b Inner cylinder 3b1 Rib 3b2 Step part 3c Opening part 4 Erase holder 4a Small diameter part 4b Large diameter part 5 Knock button 6 Eraser 7 Sleeve 7a Annular wall 7b Protruding part 11 Core pipe 12 Chuck 12a Base part 12b Beam-like part 12c Swelling part 13 Chuck ring 15 Chuck spring 18 Synthetic cushion spring 18-1 First winding part 18-2 Second winding Part 18A Synthetic cushion spring 18A-1 First cushion spring 18A-2 Second cushion spring 30 Flop 31 guide pipe 31a inserted leg 31b proximal portion 32 core holder 32a slits 36 return spring 38 O-ring

Claims (5)

A barrel,
A chuck mechanism housed in the shaft cylinder, which can grip and send out a writing core;
First and second cushion springs that elastically support the chuck mechanism with respect to the shaft cylinder in the axial direction;
By combining the first and second cushion springs, a first cushion operation region having a first spring constant and a second cushion operation region having a second spring constant are formed, and the first A mechanical pencil characterized in that the first and second cushion operation areas are connected without jumping. The mechanical pencil according to claim 1, wherein the first and second cushion springs are integrally formed as a coil spring having first and second winding portions. The mechanical pencil according to claim 1 or 2, wherein the first and second cushion springs are attached with a free length. The first cushion operating region and the second cushion operating region are such that the combined first and second cushion springs are 0.45 ± when a writing pressure is applied in a range of 150 ± 50 g. The mechanical pencil according to any one of claims 1 to 3, wherein the mechanical pencil is connected at one operating point that contracts within a range of 0.15 mm. The second cushion operating region is a region in which the combined first and second cushion springs contract in a range of 0.8 ± 0.11 mm when a writing pressure is applied in a range of 350 ± 50 g. The mechanical pencil according to any one of claims 1 to 4, comprising an operating point.

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